Sometimes outlook files become corrupt and/or Outlook begins to act slow. In case that outlook needs to be reset, the first think to try is to delete the identity. If you’re using exchange, this isn’t a problem because all your emails should be stored on the exchange server.

So, to delete your current identity, close down outlook and re-launch it while holding down the *option* key. The Microsoft Database Utility will open up and you should be able to select and delete your identity

Below are some more detailed instructions, including how to back up your identities folder before deleting: